FIG. 2.

Interassay reproducibility across assay duration and cell lines. Interassay reproducibility was assessed using a regression analysis with general linear models, taking into account all N-9 concentrations. Low reproducibility was indicated where the variability between replicates was higher than the variability within replicates and was significant (P < 0.05) when the F ratio was greater than approximately 3.0 (PROC GLM, SAS 2004). *, F ratio equals the variability in experimental measures between replicates divided by the variability in experimental measures within replicates. The horizontal line indicates the approximate F value that would result from a significant replicate effect when P was <0.05.